I saw a white head appear in a hollow used by Sulphur-crested Cockatoos in previous breeding seasons. The cockatoo came all the way out and started chewing at the wood around the hollow. It even used its claws and beak to lower itself down below the hollow to chew at the bottom of the hollow before climbing back into the opening. A second cockatoo arrived behind the hollow while the first bird was inspecting it. The initial bird climbed onto the top of the tree branch to chase away the newcomer. The interloper did not go too far, just to a different nearby branch but it eventually departed the area. The original bird returned to the hollow and to chewing at the wood.